Hi all,

I have a project in my hand and I need guru’s advise(s) on that.

A PLC system where 4 current sources will be converted to digital format, manupulate the digital data and output on a 7 segment LED display in numerics.

Details:
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Input:
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Input (1) , (2) and (3) = variable current source from 4~20mA, at 10V (approx).
Input (4) a constant current source 18.25mA at around 10V.



Process:
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The all above 4 inputs will be converted from Analogue to digital format.

The output in digital format = 0.0807 X (a) X input (3)

Whereas (a) = input (1) X input(2) / Input (4).



Output:
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Output is required with 3 whole digits and one digit after decimal.


My Idea:
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I think I should do current to voltage conversion for all 4 signals, and that voltage output should be produced to A/D input.

Process the digitized value as described above and convert the result into BCD, then display it on 7 segments.


I request all gurus, Peter, Steve, Jay, Alan and all experienced masters to help me determining the:

1- what is the right practical method for current to voltage converter, I have to use Op-amp, but which one???

2- What sort of 8051 derivative should I use that support built-in A/D converter, Please help me finding the right part.

3- Any other suggestion or link ???

Thanks

Rauf